A typical silent chain for use in power transmission is composed of guide link rows, each comprising a pair of guide plates and a plurality of intermediate link plates disposed between the guide plates, and non-guide link rows, each comprising a plurality of inner link plates. The guide link rows and non-guide link rows are disposed alternately along the length of the chain, and the plates of the guide link rows are interleaved with the plates of the non-guide link rows and connected by connecting pins so that interconnected link rows can articulate relative to each other. Each of the connecting pins can be composed of a long rocker pin and a short rocker pin, having facing rocker surfaces. The long rocker pins are fitted into front and rear holes in the guide plates. Each link plate other than the guide plate has a pair of holes, one of which can be a front hole and the other of which can be a rear hole, the terms “front” and “rear” referring to the direction in which the chain ordinarily moves when in operation. A pair of rocker pins consisting of a long pin and a short pin extends through each of these holes.
In the conventional silent chain 500 shown in FIG. 5, link plates 520 are arranged in guide link rows. Each plate 520 has a pair of teeth and a pair of link pin holes. Link plates 530 are arranged in non-guide link rows. The rows of plates 520 and 530 are pivotally linked by pairs of long and short rocker pins 541 and 542, the pins of each pair having mutually facing rocker surfaces. The pairs of pins extend through front and rear holes of the link plates and the long pins 541 tightly fit into pin holes in guide plates 510 disposed at opposite ends of each of the guide link rows.
Intermediate portions of the guide plates 510 at the opposite ends of each guide link row are formed so that they can overlap both sides of a sprocket tooth and thereby prevent the chain from deviating in the direction of the width of the sprocket.
In operation, tension is imparted directly to the link plates 520 and 530 by the sprocket with which the chain is engaged. However, guide plates 510 are not brought into tension directly by the sprocket teeth directly.
By reason of the slight clearances between the link plates and the rocker pins, and because of their elastic deformation, central parts of the long rocker pins 541 deform while both ends are restricted by the guide plates 510. As shown (with exaggeration) in FIG. 6, the long rocker pins become arcuate in shape, and the guide plates 510 also warp, becoming arcuate in shape.
As a result of the bending of the long rocker pins, the link plates 520 and 530 abut the rocker pins 541 and 542 butt unevenly and tension becomes concentrated locally, reducing the overall tensile strength of the silent chain, increasing elongation of the chain due to excessive wear, and increasing heat and noise due to repetitive deformation.
The deformation described above allows a longitudinal shifting of the link plates 520 and 530, which results in variations in the effective tooth pitch of the chain. The variations in the effective tooth pitch make seating of the teeth unstable, which can cause jumping of the teeth and increased noise.
U.S. Pat. No. 6,383,105, dated May 7, 2002, reduces deformation of the long rocker pins and warping of the guide plates by the use of guide plates which deform in the direction of chain tension. However, guide plates described in U.S. Pat. No. 6,383,105 are unable to prevent deformation of the long rocker pins, and warping of the guide plates fully. The reason is that the front edges of the front pin holes and the rear edges of the rear pin holes of the guide plates are aligned with corresponding front and rear edges of the pin holes of the intermediate link plate when the chain is in an unloaded condition. As a result, tension applied to the chain can still produce a stress causing the link pins to bend and the guide plates to deform.
Another problem with known chains having guide plates that deform in the direction of chain tension is that the angles of the front edges of the front connecting pin holes and the rear edges of the rear connecting pin holes in the guide plates change as the guide plates deform. When these angles change, the shapes of the connecting pin holes in the guide plates do not correspond to the shapes of respective front edges of the front pin holes and rear edges of the rear pin holes in the intermediate link plate. Consequently, the long rocker pins come into point-to-point contact with part of the front and rear link pin holes of the intermediate link plates, generating biased loads, wear, and increased heat and noise.